Diencephalon

commissure • Divisible in to:

Thalamus Hypothalamus Subthalamus Epithalamus Metathalamus

• From interventricular foramen to posterior

Thalamus • Large mass of grey matter, lateral to 3rd ventricle. • Processes the affarent impulses to cerebral cortex. • Reciprocal connections with cerebral cortex & subcortical

grey masses. • Anterior & posterior ends • Surfaces: Medial- lined by ependyma; forms lateral wall

of third ventricle; interthalamic adhesion; hypothalamic sulcus Superior- anterior tubercle; related to fornix, stria terminalis, caudate nucleus. Inferior- related to hypothalamus anteriorly, to subthalamus posteriorly; post. Surface exhibits twoswellings- MGB & LGB. Lateral- in contact with internal capsule.

divides it in to

Thalamus- internal structure

• Stratum zonale • External medullary lamina • Internal medullary lamina-

Anterior- anteroventral, anterodorsal,anteromedial

Medial- Dorsomedial Lateral-Dorsal- lateral dorsal, lat. Posterior,

pulvinar Ventral- ventral anterior, ventral lateral,

ventral posterior

Thalamic nuclei-contd.

• Midline nuclei- closely associated with interthalamic adhesion; concerned with visceral activity; connected to hypothalamus, dorsomedian & to intralaminar nuclei.

• Intralaminar nuclei- separate medial & lateral nuclei. Main nuclei-centromedian, parafascicular; affarents from reticular formation, fore brain, pallidal; efferent to putamen.

•Anterior nucleus:

Mamillary body AN cingulate gyrus

(mamillothalamic tract)

• Dorsomedial nucleus: Amygdaloid body DM cingulate gyrus, parietal

lobe, prefrontal cortex Globus pallidus piriform lobe

Ventral group •Ventral anterior: Globus pallidus VA Premotor & motor c. cortex

•Ventral lateral- sub. nigra, GP, precentral C.C VM precentral C. C. •Ventral Posterior: Ventral Posteromedial (VPM) (largest somatic relay) Ventral posterolateral (VPL) Medial lemniscus VPL Sup. Thalamic radiations Sensory C. Cortex (3,1,2) Spinothalamic tract VPL ( post. Limb of Int. capsule)

Trigemino-thalamic Solitariothalamic VPM Sensory Cerebral Cortex (3,1,2)

Lateral Group •Lateral dorsal •Lateral posterior •Pulvinar

Superior colliculus LD, LP, P sup. Parietal lobule, cingulate gyrus, parahippocampal & hippocampus, Parietal area

Retina P association visual area

Afferent connections 1. Spinothalamic tract

Medial lemniscus Trigemino-thalamic Solitariothalamic

2. Optic tract 3. Auditory pathway 4. Mamillothalamic tract 5. Cerebellar fibres 6. Corpus striatum &

globus pallidus 7. From cerebral cortex

Thalamic radiations (efferent)

1. Anterior (frontal)

2. Superior (centroparietal)

3. Posterior (occipital)

4. Inferior (temporal)

Hypothalamus

• Below the thalamus, forms lower lateral wall of 3rd ventricle.

• Laterally in contact with internal capsule & subthalamus.

• Posteriorly merges with subthalamus. • Anteriorly extends up to lamina terminalis. • Inferiorly related to structures in floor of 3rd

ventricle. • Medial and lateral zones

Afferent connections

1. From spinal cord & brainstem (via reticular formation)

2. Nucleus of tractus solitarius 3. Olfactory pathways 4. Limbic system 5. Locus coeruleus 6. From piriform cortex, orbital cortex 7. From subthalamus & zona incerta

Efferent connections 1. To autonomic centres in brain stem and spinal cord e.g.

tractus soiltarius, dorsal nucleus of vagus, nucleus ambiguus, intermedio-lateral grey column.

2. To hippocampal formation, septal nuclei, amygdaloid complex, tegmentum.

3. To anterior nucleus of thalamus (mamillothalamic tract) 4. To subthalamus & tegmentum (mamillo-tegmental tract) 5. To neocortex 6. Control of pituitary gland

- neurosecretion - release of vasopressin (ADH); oxytocin - control of post. Neurohypophysis - production of releasing factors (tubero-hypophyseal) - hypothalamo-hypophysial portal system

Functions

1. Regulation of eating & drinking behaviour 2. Regulation of sexual activity & reproduction 3. Control of autonomic activity 4. Control of endocrine system 5. Emotional behaviour 6. Response to stress 7. Temperature regulation 8. Biological clock

Epithalamus • Visceral efferent pathway to convey

impulses to brain stem. • Pineal body • Habenular trigone • Stria medullares

Pineal body • Cone shaped body attached to roof of 3rd ventricle • Rudimentary gland • Richly vascular connective tissue along with glia cells and

pineal cells. • Receives fibres from stria medullares, habenular nuclei &

post. Com. • Inhibits gonadal function. • After 16 yrs., calcerous bodies present which are visible in

skull x-rays. • Identification & position of pineal gland in skull films.

Metathalamus

• Medial geniculate body • Lateral geniculate body

Lateral geniculate body

Subthalamus • Lies below post. part of thalamus • Inferiorly continuous with tegmentum • Laterally related to internal capsule • Reticular nucleus: separated from thalamus. somatic, visceral, auditory, reticular formation send afferents to reticular nucleus which connects to dorsal part of thalamus.

• Zona incerta: connected to reticular nucleus; function not known.

• Subthalamic nucleus: closely related to zona incerta on one side and red nucleus on the other side. Subthalamic fasciculus pass to globus pallidus.

Applied anatomy • Lesions of thalamus: sensory loss

thalamic pain thalamic hand abnormal involuntary movements

• Subthalamic lesions: sudden, forceful, jerky/violent involuntary movements in a contralateral extremity.

• Pineal body: pineal tumors result in alteration of reproductive function.

• Hypothalamus: Obesity/wasting Sexual disorders Hypo/hyperthermia Diabetes insipidus Disturbance in sleep Emotional disorders